Individual electrical components of a semiconductor device were originally integrated on a silicon wafer by forming a vertical back to back diode between the components. This was done by forming a lightly doped epitaxial layer (“epi” layer) over a substrate of the opposite doping type. Then a deep junction of the same type as the substrate was diffused down from the top of the epi layer to the substrate.
In this way two back to back diodes were formed from the epi layer on one side of the deep junction to the epi layer on the other side. Because the junction had to be driven all the way down through the epi layer to the substrate, and because the diffusion process proceeds in all directions, this method required a great deal of space to implement. Because the electrical components must be spaced away from the heavily doped junctions there had to be sufficient space provided for the lateral diffusion of the junction as the junction was driven down to the substrate. The back to back diode method did, however, provide a way to connect the front of the wafer to the substrate.
The local oxidation of silicon (LOCOS) method was also later used to isolate the individual electrical components in a semiconductor wafer. The LOCOS method, however, only provides surface isolation. Therefore, electrical components that require deep isolation are not isolated using the LOCOS method.
Shallow trench isolation has been used to replace the LOCOS method of isolation. Shallow trench isolation provides isolation in a more space efficient manner than LOCOS isolation. But because LOCOS isolation only provides surface isolation an additional method is required to provide deep isolation. Typically, when deep isolation is required, a deep trench is used in conjunction with a shallow trench. The combination of the deep trench and the shallow trench does not provide a method of connecting to the substrate.
Therefore, there is a need in the art for a system and method for providing a deep connection to a substrate or buried layer of semiconductor device. There is also a need in the art for a system and method for combining shallow trench isolation with partial deep diffusion to provide a deep connection to a substrate or buried layer of a semiconductor device.